Here are some thoughts on how I would go about getting this working.
I'd start by trying to get a simple-as-possible wgpu-rs example that has already been demonstrated to work well in the browser locally, to verify that it's at least possible on my setup. Keep in mind that the current nannou master uses wgpu 0.5, so it might be worth testing the wgpu example with 0.5 too. Alternatively, if it seems like wgpu 0.6 is needed, #655 looks to be most of the way there (haven't had a chance to do a full review just yet).
Once working, I would try to make a copy of the example, and add nannou as a dependency. Doing this should include nannou in the build process for the WASM target, and any remaining issues should be raised by the compiler as an error. There shouldn't be any major blockers, but this will help to guide towards what remains that needs addressing.
The wgpu-users channel on Matrix is also full of very helpful folks - I highly recommend hanging out there while hacking on this :) They've been a great help in landing wgpu in nannou in general.
I hope some of this helps a little bit!